Gaseous rectifier



July 27, 1937. P, L SPENER 2,088,249

GASEOUS RECTIFIER Original Aug. -4, 2 s s l INVENTOR Pmcr SPiA/cfl?ATTOR EY July 27, 1937. P. L. SPENCER [2,083,249

GASEOUS RECTIFIER Original'Filed Aug. 4, 1951 2 s s 2 INVENTOR Pmcy L5PE/VCf/Q ATTO Patented July 27, 1931 UNITED STATES PATENT OFFICE IGaseous RECTIFIER Percy L. Spencer, West NcwtonQMasa, assignor,

by mesne assignments to Raytheon Mannfacturing Company, Newton, Mass., acorporation of Delaware Application August '4, 1931, Serial No. 555,005Renewed November 21, 1936 4 Claim.

erence being had to the accompanying drawings, wherein:

Fig. l is a cross-sectional view of one embodi- 15 ment of my invention;

Fig. 2 is a section taken along line 2--2of Fig. 1;

Fig. 3 is a cross-section of another embodiment of my invention; and. 20Fig. 4 is a section taken along line l4 of Fig. 3. i

In rectifiers which operate with an ionizing discharge through a gas, itis desired to conduct electricity through the gas when the' cathode iswhen subjected to an alternating voltage havev broken down in thenon-conducting or reverse- 3 direction at voltages considerably lowerthan such a rectifier would be able to withstand if a direct voltagewere initially impressed across the anode and the cathode in saidreverse direction. This breakdown discharge usually occurs 40 betweenthe cathode and anode leads as they enter the sealed bulb from thepress. According to my present understanding of the phenomena involved,breakdown discharges of the above kind occur for the following reasons.

45 In allgases and, vapors there exists a number of free electrons evenunder conditions where no outside electrical stress is impressed on saidgases and vapors. When a voltage is applied across such an atmosphere,as for example the 50 atmosphere between the anode and'cathode leads ofa rectifier, the free electrons will be accelerated by the voltage. Ifthe voltage is large enough, the electrons will attain suflicientvelocity to ionize a neutral atom upon collision there- 55 with, therebyliberating additional electrons.

negative and the anode is positive, while,when

When the number of electrons so liberated reaches a sufliciently largenumber, the resistance of the atmosphere to the passage of an electricalcurrent falls to a very low value and a breakdown discharge will occur.The voltage 5 which gas or vapor can withstand without breakdowndecreases with an increase in the number of free electrons in that gasor vapor. As pointed out above, there are always some free electronspresent in such atmospheres. How- 10. ever, if the normal number ofelectrons is increased by electron emission from any of the memberswithin the atmosphere, such as, for example, the electrode leads, thebreakdown volt- .age decreases. Emission from the anode lead isparticularly effective in causing breakdown in the reverse direction ina rectifier. This is due to the fact that an electron emitted from theanode lead when the cathode is positive, will be attracted to thecathode and must pass through the gas or vapor in the intervening space.An electron emitted from the cathode lead under such conditions willimmediately fall back on the cathode lead without having a chance toionize any of the gas atoms.

I have discovered that electrons may be emitted from the anode lead, dueto the following reasons. When an ionizing discharge occurs in a gaseousatmosphere, such as, for example, mercury vapor, a large number of atomsin the discharge space become excited and radiate the characteristicradiation of that gas which in mercury is of a wave length of 2536Angstrom units. In ordinary rectiflers. this radiation diffuses throughthe gas within the tube, and is absorbed by atoms of that gas which inturn become excited. When an excited atom collides with the surface ofsome member, such as an anode or cathode lead, it is extremely likely toknock out an electron from that surface, due to the excitation energywhich the atom possesses. The tendency to knock out an electron is verymarked when the work function of the surface with which the excited atomcollides is less than the excitation voltage of the excited atom. Thisrelation usually exists between the work function of the cathode andanode leads and the excitation voltage of the gas filling in the tube.For example, in the case where nickel wires are used as the electrodeleads and mercury vapor as the gas filling, the excitation voltage ofthe mercury atom is 4.9 volts while the work function of the nickel is4.1 volts. Thus the nickel wires will often emit an electron when anexcited mercury atom collides with the surface of said nickel wires. Theelectron emission is also increased when the temperature of the wires isallowed to increase. In a rectifier, excitation of the gas atomsordinarily occurs during the conducting half cycle, and ceases when thepolarity reverses and the tube becomes non-conducting. However, it takesan appreciable length of time for the radiation to diffuse out of thegaseous atmosphere. This diffusion takes place, at least partly, by thefollowing mechanism. An excited atom persists in its state of excitationfor an appreciable length of time. The average length of time in whichan excited atom persists in its excited state, in the case of mercuryvapor, is 10 seconds. Since the atom possesses a definite averagevelocity dependent upon the temperature of the gas, it will travel a.definite average distance during this time, after which it will emit thecharacteristic radiation. This radiation will travel out from the atom,and will be absorbed by a neighboring atom. This neighboring atombecomes excited, and likewise persists in the excited state for the samedefinite average length of time. This transmission of radiation fromatom to atom continues until it is lost either by the radiation passingout through the walls of the tube, by being absorbed by the surfaces ofthe tube, or the surfaces of the electrode structure within said tube,or by an excited atom colliding inelastically with another atom or withone of the above surfaces. It will be appreciated that the length oftime which it takes for the radiation to diffuse out of the gas isgreater when the amount of gas through which it can diffuse is greater.When the radiation is allowed to diffuse through the whole tube, such asoccurs in the ordinary rectifier tube, this time is so great that thereare still an appreciable number of excited atoms within the gas when thereverse potential is applied between the electrodes. The presence ofthese excited atoms causes an appreciable number of electrons to beliberated from the electrode leads, as explained above. This number ofatoms is sufficient to initiate a breakdown discharge between the leadswhen a voltage of suflicient value is impressed across them. However, ifthis liberation of electrons did not occur, a considerably greatervoltage could be impressed across said elements without the dischargetaking place.

In accordance with my invention, I eliminate the above cause of thebreakdown of the rectifying tube by confining the radiation due to thedischarge in a limited space, and by shielding the electrode leadsagainst said radiation. I also find that the arrangement which I useproduces a considerable increase in the efficiency of my rectifier.

Referring to Figs. 1 and 2, which show one embodiment of my invention,my rectifier comprises a sealed glass envelope I, having a reentrantstem 2 formed with a press 3 at its upper end. Anode lead 4 sealed insaid press supports an anode 5. This anode is preferably constructed ofcarbon. Cooperating with the anode 5 is a thermionic cathode 6. Thiscathode preferably comprises a metallic filament, such as, for example,nickel coated with some material to increase the electron emissivity ofsaid filament. Such a coating may consist of barium or strontium oxide.The filament 6 is sup.- ported by two filament leads 8 and 9. Thefilament 6, as shown, preferably consists of a flat ribbon which isdisposed edgewise with respect to the anode 5. The anode 5 is in theform of a disk in a position between the thermionic cathode 6 and thepress 3, so that said press and the wires sealed therein are shieldedagainst any direct radiation coming from the discharge between the anode5 and the cathode 6. In order to more completely shield the wires sealedin the press 3, a cap I0 is placed over the thermionic cathode 6. Thecap 10 and anode 5 cooperate so as to practically entirely confine theradiations generated by the discharge between the electrodes. The cap I0is supported by means of a standard ll sealed in the press 3. Thecathode lead 8 is welded to the standard H while the cathode lead 8 isalso sealed in the press 3. A getter cup i2 which originally contains amixture which liberates barium on heating may be supported from one ofthe wires sealed in the press 3, for example, the cathode lead 8. Thevarious parts within the envelope are freed from occluded gases, andsaid envelope is evacuated in accordance with the usual practice. Aquantity of mercury i3 is placed in the tube in order to furnish thedesired mercury vapor atmosphere. The barium is freed from the gettercup l2, for example by inductive heating thereof. This barium cleans upthe various residual impurities which exist in the tube, and some of thebarium also amalgamates with the mercury. This barium amalgamated withthe mercury acts continually as an active getter to clean up anyimpurities which may subsequently be liberated within the envelope I.The envelope I may be provided with the usual base I4 carrying contactprongs i5, i6 and H. The lead 8 and the standard II are provided withconductors which are connected to contact prongs l5 and 16,respectively, while the anode lead 4 is connected to contact prong IT.The rectifier as described may be connected to a suitable rectifyingcircuit which may be, for example, such as that shown in Fig. 1. Thecathode 6 is provided with heating current from a section [8 of thesecondary of a transformer 19. A source of relatively higher potentialis impressed between the cathode 6 and the anode 4 by another section 20of the secondary of said transformer l9. Some load device, indicated at2|, is connected in series in the cathode-anode circuit. The transformerI9 is provided with a suitable primary winding 22 which is connected toa source of alternating current.

When the rectifier is connected, as shown in Fig. 1, the section l8 willfurnish heating current to the filament 6 which will be raised to atemperature at which it emits a large number of electrons. When thepotential, due to the section 20 of the transformer, is in such adirection as to make the cathode 6 negative and the anode 5 positive,electrons coming from the cathode 6 will travel toward the anode 5. Theelectrons traveling in this direction will collide with the atoms ofmercury which will exist throughout the tube, due to the presence of themercury Hi. The energy which these electrons will have gained, due tothe potential between the electrodes, will usually be sufficient tocause the atoms with which they collide to be ionized. Thus, largenumbers of electrons and positive ions will exist between the cathodeand anode, and enable a large amount of current to pass with acomparatively low voltage drop. However, some of the atoms will not beentirely ionized, but will be put into an excited condition. Theseexcited atoms will emit the radiation of A 2536, the resonant radiationof the mercury atom. This radiation will diffuse throughout the vaporenclosed by the cap l0 and the anode 5. Due to the configuration ofthese elements,.very little radiation will be allowed to escape from thespace enclosed by said elements.

Within the cap Ill some of the excited atoms will collide with thesurface of said cap, and liber- -ate electrons therefrom in accordancewith the explanation given in the early part of thespecification. Duringthe handling and operation of the device there may be a tendency forsome of the barium to deposit upon the metallic surfaces with which itcomes in contact, and thus some barium may be deposited upon the insidesurface of the cap l0. Also any of the coating which is dislodged fromthe filament 6 during operation likewise tends to deposit upon theinside surface of the cap Ill. These deposits lower the work function ofthe cap I0, and thus electrons are much more easily emitted from saidcap upon bombardment by excited atoms. The configuration of the partsalso tends to raise the' temperature of the inside surface of the cap H)to such a degree that some electrons are thermionically emitted from thebarium-coated inner surface of said cap. Even without the presence ofbarium, the inner surface of the cap l0 emits a considerable number ofelectrons, yet the presence of the barium itself causes said cap tobecome a very good emitter of electrons. If the inside surface of saidcap is oxidized, itsaffinity for the barium is greatly increased, and insome instances it may be desirable to so oxidize said surface. In orderto take advantage of the electron emission of the cap l0, said cap iselectrically connected to the cathode 6 by having the cathode lead 9connected to the cap standard ll.

Due to the fact that the radiation is confined V to the volume withinthe cap, a larger number of excited atoms perunit volume will existwithin said volume than if the radiation were allowed to diffusethroughout the envelope l. Thus the chance for an excited atom to absorbenergy by collision with an accelerated electron or atom, or by theabsorption of some radiant energy, is correspondingly increased. When anatom is in an excited condition, it requires but a slight additionalamount of energy to ionize that atom. Therefore, the concentration ofexcited atoms within the discharge space, due to the enclosure by thecap l0, facilitates the ionization of these atoms. Thus liberation ofelectrons from the inner surface of the cap ill and the increasedionization due to the concentration of excited atoms within said cap,enable the same amount of current to be drawn between the cathode andthe anode with a lower voltage drop than would ordinarily be necessary.Therefore the losses are decreased and the efficiency of the tube isincreased. l

When the potential impressed between the anode 5 and the cathode 6reverses in direction cap I0 and the remaining structure surroundingsaid'confined space takes place in a comparatively short interval oftime. By the time the voltage between the .anode 5 and the cathode 6reaches a value which would be sufllcient to start a discharge if anappreciable number of electrons were being liberated from the anodestructure, the radiation will have diffused to such an extent that aninsignificant number of excited atoms are colliding with the anodestructure. It should be noted, moreover, that the anode being made ofcarbon has a work function which is higher than the excitation voltageof the. mercury vapor. tie on such an anode, or if it does settle, itappears to be continually knocked off during the discharge. At allevents, the tendency for electrons to be emitted from such anode, due tothe bombardment by excited atoms, is comparatively slight. The chiefadvantage of the confining of the radiation by the cap In in thestructure shown in Fig. 1 during the inactive half cycle is that theanode lead 4 is shielded against bombardment by excited atoms. While thebarium does not tend to settle on the anode 5 itself, yet it will bedeposited upon the anode lead' 4. Furthermore, since this anode lead isusually constructed of a metal, such as nickel, the work function ofthis lead is less than the excitation voltage of a mercury atom. Thepresence of barium on this lead lowers this work function still further.If excited atoms were allowed to collide with this lead during theinactive half cycle, a sufficient number of electrons would be liberatedfrom said lead to initiate a breakdownxdischarge for certain values ofreverse voltage. However, the structure as shown in Fig. 1 effectivelyshields anode lead 4 against bombardment by excited atoms, and thereforevoltages which would otherwise produce a' breakdown can he this point,at a comparatively lowtemperature by shielding them against saidheatradiations as .well as against the characteristic radiations of v thedischarge undoubtedly is of considerable effect in preventing electronemission from the leads and in preventing breakdown discharges at thispoint. 7 g H I'have constructedrectifiers, as shown in Fig.

Furthermore, barium does not seem to set V 1 above, with and without thecap in. Without two amperes with a voltage drop of only three volts.Thus it can be seen that the shield, due to the cap I 0 results in aconsiderable increase both in the amount of backvoltage wh ch therectifier could withstand, and also in the efiiciency of said rectifier.

While the number of electronsliberated from the anode itself, due tobombardment by excited atoms, is of comparatively little importance in asingle wave rectifier, such as that shown in Fig. 1, yet this effectbecomes appreciable when a full-wave rectifier having two or more anodes.is' used. This is due to the fact that in a single wave rectifier withan arrangement as shown in Fig. 1, the radiation has been practicallyentirely diffused by the time the reverse voltage is applied. In adouble wave rectifier, however, there is a large number of excited atomspresent when a reverse voltage is applied between one anode and thecathode. This is due to the fact that when the full reverse voltage isimpressed between one anode and cathode, a discharge is occurringbetween the other anode and cathode. This discharge causes a largenumber of excited atoms to be generated, which excited atoms oncolliding with the inactive anode tend to liberate a sufficiently largenumber of electrons to cause a breakdown in the reverse direction whenthe reverse voltage is of sufficient value.

In Fig.3 I have shown an arrangement which decreases the effect ofliberation of electrons from the anodes, due to the bombardment byexcited atoms in a full-wave rectifier. Fig. 3 shows a sealed envelope3| having a reentrant stem 32 carrying a press 33 at its upper end. Thepress 33 carries the electrode structure, including two anodes 34 and 35and a cathode 36. The anodes 34 and 35 are preferably formed of carbon,and are supported respectively by anode leads 3! and 38 sealed in thepress 33. The press 33 carries glass tubes 39 and 40 surrounding theanode leads 3'! and 38, respectively, as they emerge from said press.The upper ends of the tubes 39 and 40 carry insulating tubes 4| and 42,respectively. Each of these insulating tubes is formed with a centralhole through which the anode leads pass. A hollow member 43 enclosingthe anodes 34 and 35 and the cathode 36 rests upon the upper ends of theinsulating tubes 4| and 42. This hollow member is formed of thin metal,such as, for example, nickel or iron, and is provided in its lower wallwith apertures in line with the openings in the glass and insulatingtubes through which the anode leads 31 and 38 pass into the interior ofsaid hollow member. The spacing between the anode leads and the openingsin the wall of the hollow member 43 may be of the order of the mean freepath of the gas in the tube in accordance with the patent to Smith, No.1,617,179. The cathode 36 may be a. thermionic filament of the kind asdescribed for Fig. 2, and is positioned intermediate the two anodes 34and 35. This cathode is supported at its opposite ends by two standards44 and 45 which pass through openings in the bottom wall of the hollowmember 43. One of the standards 44 may be electrically connected withthe hollow member 43 by a connecting member 46. This member ispreferably welded to both the standard 44 and the bottom wall of thehollow member 43. This arrangement also serves to help support thecathode. The standards 44 and 45 are connected respectively to twocathode leads 4'! and 46 sealed in the press 33. The hollow member 43 isalso firmly supported in the proper position by two standards 43 and 58also sealed in the press 33. A getter cup 5| may be supported within theenvelope 3| by being welded to one of the standards, for example 49. Theanodes 34 and 35 are provided respectively with shields 52 and 53. Theseshields are in the form of cups so positioned that the open side thereoffaces away from the cathode 36 and the other anode. These shields may beformed of any material opaque to the radiations generated by thedischarge, but are preferably formed of a thin metal, such as nickel oriron. The shields are provided with an opening in one side thereof forthe passage of the cathode leads 31 and 38, and are welded to the bottomwall of the hollow member 43 in such a position that the anode leads maypass through said openings. As described for Fig. 1, envelope 3| isprovided with a quantity of mercury 54 after the tube has beenthoroughly freed of occluded gases, and has been evacuated in the usualmanner. The getter cup 5| may contain a source of barium as does gettercup l2. The envelope 3| is provided with a base 55 carrying four contactprongs 56, 51, 58 and 59. The anode leads 31 and 38 are connectedrespectively to the contact prongs 56 and 59 while the two cathode leads4! and 48 are connected respectively to the two contact prongs 51 and58.

The tube as described in Fig. 3 may be provided with any suitableoperating circuit, one of which may be as illustrated diagrammaticallyin Fig. 3. A source of heating current for the oathode 36 consists of atransformer 60 connected between the two contact prongs 51 and 58. Asource of relatively higher potential is connected between the two anodeleads 56 and 58. This source may consist of a secondary 6| of atransformer 62, the primary 63 of which is connected to a suitablesource of alternating current. A connection is provided between themidpoint of the secondary 64 of the transformer 60 and the midpoint ofthe secondary 6|. In this connection is placed any desirable load asindicated at 65.

The operation of the device, as shown in Fig. 3, is very similar to thatas described for Fig. 2. It will be noted that the anode leads are veryeffectively shielded against bombardment by excited mercury atoms. Inaddition, however, each of the anodes is also shielded against such bombardment. When discharge occurs between one of the anodes, for example34, and the cathode 36, such a discharge will cause radiations to begenerated along the path of the discharge which extends from the cathode36 around the edges of the shield 52 to the anode 34. Liberation ofelectrons may occur from the surface of the shield 52 as well as fromthe hollow member 43, due to the bombardment by excited atoms, asexplained in reference to Fig. 2. Since each of these members iselectrically connected to the cathode 36, the liberation of electronstherefrom will increase theefliciency of the rectifier. During suchdischarge it will be noted that the shield 53 and the adjacent wall ofthe hollow member 43 effectively shield the anode 35 against theradiations generated by the adjacent discharge. The number of excitedatoms which will reach the surface of the anode 34 will be very small,due to the above arrangement. Due to the small number of excited atomscolliding with the surface of the anode 35 and due to the fact that thissurface has a comparatively high work function, an insignificant numberof electrons will be liberated from the anode 35 during said adjacentdischarge. Upon reversal of potential, the discharge will shift from theanode 34 to the anode 35. However, the anode 34 will be protected by theshield 52 in the same manner as the anode 35 was protected by the shield53.

It will be noted that the anodes 34 and 35 as well as their leads arealso effectively shielded against heat radiations from the cathode 36.This shielding enables the anodes and their leads to be operated atcomparatively low temperatures which further diminishes the possibilityof electrons being emitted from either said anodes or their leads.

The arrangement as shown in Fig. 3 will enable the rectifier to operateat considerably higher voltages and with increased efiiciency.

This invention is not limited to the particu lar'details ofconstruction, materials or processes described above, as manyequivalents will suggest themselves to those skilled'in the art.

It is accordingly desired that the appended claims be given a broadinterpretation commensurate with the scope of the invention within theart.

What is claimed is:

1. A space discharge device comprising a gastight envelope containing anionizable atmosphere, an anode, and a thermionic cathode, said cathodeand anode being adapted to support an ionizing discharge between them,said cathode comprising an electron-emitting filament consisting of aflat conductor and a hollow conducting member electrically connected toand surrounding said fiat conductor, and an opening of substantial sizein said hollow member, said anode having a surface of relatively highwork function substantially closing said opening to prevent radiationsand material liberated by the discharge from escaping from the spaceenclosed by said hollow member and said anode, said fiat conductor beingdisposed edgewise with respect to said anode, all of the dischargeswhich occur in said device being confined to the space enclosed by saidhollow member and anode.

2. A space discharge device comprising a gastight envelope containing anionizable atmosphere, an anode and a thermionic cathode, said cathodeand anode being adapted to support an ionizing discharge between them,said cathode comprising a filament coated with a solid electron emissivecoating adapted to be heated to a temperature of thermionic emission,and a hollow conducting member electrically connected to and surroundingsaid coated member, an opening in said hollow member, said anode beingdisposed outside of said hollow member and having a surfacesubstantially blocking said opening.

3. A space discharge device comprising a gastight envelope containing anionizable atmosphere, an anode, and a thermionic cathode, said cathodeand anode being adapted to support an conducting member electricallyconnected to and.

surrounding said flat conductor, and an opening of substantial size insaid hollow member. said anode having a surface of relatively high workfunction substantially closing said opening to substantially preventradiations and material liberated from the discharge from escaping fromthe space enclosed by said hollow member and said anode, substantiallyall of the discharges which occur in said device being confined by thespace enclosed by said hollow member and anode.

4. A space discharge device comprising a gastight envelope containing anionizable atmosphere, an anode, and a thermionic cathode, said cathodeand anode being adapted to support an ionizing discharge between them,said cathode comprising an electron-emitting filament consisting of afiat ribbon conductor, said conductor being crimped and wound in such away as to increase the total length of filament within a predeterminedspace, a hollow conducting member electrically connected to andsurrounding said flat conductor, and an opening of substan tial size insaid hollow member, said anode having a surface of relatively high workfunction substantially closing said opening to substantially preventradiations and material liberated from the discharge from escaping fromthe space enclosed by said hollow member and said anode, substantiallyall of the discharges which occur in said device being confined by thespace enclosed by said hollow member and anode.

PERCY L. SPENCER.

